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6: <h1>pcrejit man page</h1>
7: <p>
8: Return to the <a href="index.html">PCRE index page</a>.
9: </p>
10: <p>
11: This page is part of the PCRE HTML documentation. It was generated automatically
12: from the original man page. If there is any nonsense in it, please consult the
13: man page, in case the conversion went wrong.
14: <br>
15: <ul>
16: <li><a name="TOC1" href="#SEC1">PCRE JUST-IN-TIME COMPILER SUPPORT</a>
1.1.1.2 ! misho 17: <li><a name="TOC2" href="#SEC2">8-BIT and 16-BIT SUPPORT</a>
! 18: <li><a name="TOC3" href="#SEC3">AVAILABILITY OF JIT SUPPORT</a>
! 19: <li><a name="TOC4" href="#SEC4">SIMPLE USE OF JIT</a>
! 20: <li><a name="TOC5" href="#SEC5">UNSUPPORTED OPTIONS AND PATTERN ITEMS</a>
! 21: <li><a name="TOC6" href="#SEC6">RETURN VALUES FROM JIT EXECUTION</a>
! 22: <li><a name="TOC7" href="#SEC7">SAVING AND RESTORING COMPILED PATTERNS</a>
! 23: <li><a name="TOC8" href="#SEC8">CONTROLLING THE JIT STACK</a>
! 24: <li><a name="TOC9" href="#SEC9">JIT STACK FAQ</a>
! 25: <li><a name="TOC10" href="#SEC10">EXAMPLE CODE</a>
! 26: <li><a name="TOC11" href="#SEC11">SEE ALSO</a>
! 27: <li><a name="TOC12" href="#SEC12">AUTHOR</a>
! 28: <li><a name="TOC13" href="#SEC13">REVISION</a>
1.1 misho 29: </ul>
30: <br><a name="SEC1" href="#TOC1">PCRE JUST-IN-TIME COMPILER SUPPORT</a><br>
31: <P>
32: Just-in-time compiling is a heavyweight optimization that can greatly speed up
33: pattern matching. However, it comes at the cost of extra processing before the
34: match is performed. Therefore, it is of most benefit when the same pattern is
1.1.1.2 ! misho 35: going to be matched many times. This does not necessarily mean many calls of a
! 36: matching function; if the pattern is not anchored, matching attempts may take
! 37: place many times at various positions in the subject, even for a single call.
! 38: Therefore, if the subject string is very long, it may still pay to use JIT for
! 39: one-off matches.
! 40: </P>
! 41: <P>
! 42: JIT support applies only to the traditional Perl-compatible matching function.
! 43: It does not apply when the DFA matching function is being used. The code for
! 44: this support was written by Zoltan Herczeg.
! 45: </P>
! 46: <br><a name="SEC2" href="#TOC1">8-BIT and 16-BIT SUPPORT</a><br>
! 47: <P>
! 48: JIT support is available for both the 8-bit and 16-bit PCRE libraries. To keep
! 49: this documentation simple, only the 8-bit interface is described in what
! 50: follows. If you are using the 16-bit library, substitute the 16-bit functions
! 51: and 16-bit structures (for example, <i>pcre16_jit_stack</i> instead of
! 52: <i>pcre_jit_stack</i>).
1.1 misho 53: </P>
1.1.1.2 ! misho 54: <br><a name="SEC3" href="#TOC1">AVAILABILITY OF JIT SUPPORT</a><br>
1.1 misho 55: <P>
56: JIT support is an optional feature of PCRE. The "configure" option --enable-jit
57: (or equivalent CMake option) must be set when PCRE is built if you want to use
58: JIT. The support is limited to the following hardware platforms:
59: <pre>
60: ARM v5, v7, and Thumb2
61: Intel x86 32-bit and 64-bit
62: MIPS 32-bit
1.1.1.2 ! misho 63: Power PC 32-bit and 64-bit
1.1 misho 64: </pre>
65: The Power PC support is designated as experimental because it has not been
66: fully tested. If --enable-jit is set on an unsupported platform, compilation
67: fails.
68: </P>
69: <P>
70: A program that is linked with PCRE 8.20 or later can tell if JIT support is
71: available by calling <b>pcre_config()</b> with the PCRE_CONFIG_JIT option. The
72: result is 1 when JIT is available, and 0 otherwise. However, a simple program
73: does not need to check this in order to use JIT. The API is implemented in a
74: way that falls back to the ordinary PCRE code if JIT is not available.
75: </P>
76: <P>
77: If your program may sometimes be linked with versions of PCRE that are older
78: than 8.20, but you want to use JIT when it is available, you can test
79: the values of PCRE_MAJOR and PCRE_MINOR, or the existence of a JIT macro such
80: as PCRE_CONFIG_JIT, for compile-time control of your code.
81: </P>
1.1.1.2 ! misho 82: <br><a name="SEC4" href="#TOC1">SIMPLE USE OF JIT</a><br>
1.1 misho 83: <P>
84: You have to do two things to make use of the JIT support in the simplest way:
85: <pre>
86: (1) Call <b>pcre_study()</b> with the PCRE_STUDY_JIT_COMPILE option for
87: each compiled pattern, and pass the resulting <b>pcre_extra</b> block to
88: <b>pcre_exec()</b>.
89:
90: (2) Use <b>pcre_free_study()</b> to free the <b>pcre_extra</b> block when it is
91: no longer needed instead of just freeing it yourself. This
92: ensures that any JIT data is also freed.
93: </pre>
94: For a program that may be linked with pre-8.20 versions of PCRE, you can insert
95: <pre>
96: #ifndef PCRE_STUDY_JIT_COMPILE
97: #define PCRE_STUDY_JIT_COMPILE 0
98: #endif
99: </pre>
100: so that no option is passed to <b>pcre_study()</b>, and then use something like
101: this to free the study data:
102: <pre>
103: #ifdef PCRE_CONFIG_JIT
104: pcre_free_study(study_ptr);
105: #else
106: pcre_free(study_ptr);
107: #endif
108: </pre>
109: In some circumstances you may need to call additional functions. These are
110: described in the section entitled
111: <a href="#stackcontrol">"Controlling the JIT stack"</a>
112: below.
113: </P>
114: <P>
115: If JIT support is not available, PCRE_STUDY_JIT_COMPILE is ignored, and no JIT
116: data is set up. Otherwise, the compiled pattern is passed to the JIT compiler,
117: which turns it into machine code that executes much faster than the normal
118: interpretive code. When <b>pcre_exec()</b> is passed a <b>pcre_extra</b> block
119: containing a pointer to JIT code, it obeys that instead of the normal code. The
120: result is identical, but the code runs much faster.
121: </P>
122: <P>
123: There are some <b>pcre_exec()</b> options that are not supported for JIT
124: execution. There are also some pattern items that JIT cannot handle. Details
125: are given below. In both cases, execution automatically falls back to the
126: interpretive code.
127: </P>
128: <P>
129: If the JIT compiler finds an unsupported item, no JIT data is generated. You
130: can find out if JIT execution is available after studying a pattern by calling
131: <b>pcre_fullinfo()</b> with the PCRE_INFO_JIT option. A result of 1 means that
132: JIT compilation was successful. A result of 0 means that JIT support is not
133: available, or the pattern was not studied with PCRE_STUDY_JIT_COMPILE, or the
134: JIT compiler was not able to handle the pattern.
135: </P>
136: <P>
137: Once a pattern has been studied, with or without JIT, it can be used as many
138: times as you like for matching different subject strings.
139: </P>
1.1.1.2 ! misho 140: <br><a name="SEC5" href="#TOC1">UNSUPPORTED OPTIONS AND PATTERN ITEMS</a><br>
1.1 misho 141: <P>
142: The only <b>pcre_exec()</b> options that are supported for JIT execution are
143: PCRE_NO_UTF8_CHECK, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and
144: PCRE_NOTEMPTY_ATSTART. Note in particular that partial matching is not
145: supported.
146: </P>
147: <P>
148: The unsupported pattern items are:
149: <pre>
150: \C match a single byte; not supported in UTF-8 mode
151: (?Cn) callouts
152: (*COMMIT) )
153: (*MARK) )
154: (*PRUNE) ) the backtracking control verbs
155: (*SKIP) )
156: (*THEN) )
157: </pre>
158: Support for some of these may be added in future.
159: </P>
1.1.1.2 ! misho 160: <br><a name="SEC6" href="#TOC1">RETURN VALUES FROM JIT EXECUTION</a><br>
1.1 misho 161: <P>
162: When a pattern is matched using JIT execution, the return values are the same
163: as those given by the interpretive <b>pcre_exec()</b> code, with the addition of
164: one new error code: PCRE_ERROR_JIT_STACKLIMIT. This means that the memory used
165: for the JIT stack was insufficient. See
166: <a href="#stackcontrol">"Controlling the JIT stack"</a>
167: below for a discussion of JIT stack usage. For compatibility with the
168: interpretive <b>pcre_exec()</b> code, no more than two-thirds of the
169: <i>ovector</i> argument is used for passing back captured substrings.
170: </P>
171: <P>
172: The error code PCRE_ERROR_MATCHLIMIT is returned by the JIT code if searching a
173: very large pattern tree goes on for too long, as it is in the same circumstance
174: when JIT is not used, but the details of exactly what is counted are not the
175: same. The PCRE_ERROR_RECURSIONLIMIT error code is never returned by JIT
176: execution.
177: </P>
1.1.1.2 ! misho 178: <br><a name="SEC7" href="#TOC1">SAVING AND RESTORING COMPILED PATTERNS</a><br>
1.1 misho 179: <P>
180: The code that is generated by the JIT compiler is architecture-specific, and is
181: also position dependent. For those reasons it cannot be saved (in a file or
182: database) and restored later like the bytecode and other data of a compiled
183: pattern. Saving and restoring compiled patterns is not something many people
184: do. More detail about this facility is given in the
185: <a href="pcreprecompile.html"><b>pcreprecompile</b></a>
186: documentation. It should be possible to run <b>pcre_study()</b> on a saved and
187: restored pattern, and thereby recreate the JIT data, but because JIT
188: compilation uses significant resources, it is probably not worth doing this;
189: you might as well recompile the original pattern.
190: <a name="stackcontrol"></a></P>
1.1.1.2 ! misho 191: <br><a name="SEC8" href="#TOC1">CONTROLLING THE JIT STACK</a><br>
1.1 misho 192: <P>
193: When the compiled JIT code runs, it needs a block of memory to use as a stack.
194: By default, it uses 32K on the machine stack. However, some large or
195: complicated patterns need more than this. The error PCRE_ERROR_JIT_STACKLIMIT
196: is given when there is not enough stack. Three functions are provided for
197: managing blocks of memory for use as JIT stacks. There is further discussion
198: about the use of JIT stacks in the section entitled
199: <a href="#stackcontrol">"JIT stack FAQ"</a>
200: below.
201: </P>
202: <P>
203: The <b>pcre_jit_stack_alloc()</b> function creates a JIT stack. Its arguments
204: are a starting size and a maximum size, and it returns a pointer to an opaque
205: structure of type <b>pcre_jit_stack</b>, or NULL if there is an error. The
206: <b>pcre_jit_stack_free()</b> function can be used to free a stack that is no
207: longer needed. (For the technically minded: the address space is allocated by
208: mmap or VirtualAlloc.)
209: </P>
210: <P>
211: JIT uses far less memory for recursion than the interpretive code,
212: and a maximum stack size of 512K to 1M should be more than enough for any
213: pattern.
214: </P>
215: <P>
216: The <b>pcre_assign_jit_stack()</b> function specifies which stack JIT code
217: should use. Its arguments are as follows:
218: <pre>
219: pcre_extra *extra
220: pcre_jit_callback callback
221: void *data
222: </pre>
223: The <i>extra</i> argument must be the result of studying a pattern with
224: PCRE_STUDY_JIT_COMPILE. There are three cases for the values of the other two
225: options:
226: <pre>
227: (1) If <i>callback</i> is NULL and <i>data</i> is NULL, an internal 32K block
228: on the machine stack is used.
229:
230: (2) If <i>callback</i> is NULL and <i>data</i> is not NULL, <i>data</i> must be
231: a valid JIT stack, the result of calling <b>pcre_jit_stack_alloc()</b>.
232:
233: (3) If <i>callback</i> not NULL, it must point to a function that is called
234: with <i>data</i> as an argument at the start of matching, in order to
235: set up a JIT stack. If the result is NULL, the internal 32K stack
236: is used; otherwise the return value must be a valid JIT stack,
237: the result of calling <b>pcre_jit_stack_alloc()</b>.
238: </pre>
239: You may safely assign the same JIT stack to more than one pattern, as long as
240: they are all matched sequentially in the same thread. In a multithread
241: application, each thread must use its own JIT stack.
242: </P>
243: <P>
244: Strictly speaking, even more is allowed. You can assign the same stack to any
245: number of patterns as long as they are not used for matching by multiple
246: threads at the same time. For example, you can assign the same stack to all
247: compiled patterns, and use a global mutex in the callback to wait until the
248: stack is available for use. However, this is an inefficient solution, and
249: not recommended.
250: </P>
251: <P>
252: This is a suggestion for how a typical multithreaded program might operate:
253: <pre>
254: During thread initalization
255: thread_local_var = pcre_jit_stack_alloc(...)
256:
257: During thread exit
258: pcre_jit_stack_free(thread_local_var)
259:
260: Use a one-line callback function
261: return thread_local_var
262: </pre>
263: All the functions described in this section do nothing if JIT is not available,
264: and <b>pcre_assign_jit_stack()</b> does nothing unless the <b>extra</b> argument
265: is non-NULL and points to a <b>pcre_extra</b> block that is the result of a
266: successful study with PCRE_STUDY_JIT_COMPILE.
267: <a name="stackfaq"></a></P>
1.1.1.2 ! misho 268: <br><a name="SEC9" href="#TOC1">JIT STACK FAQ</a><br>
1.1 misho 269: <P>
270: (1) Why do we need JIT stacks?
271: <br>
272: <br>
273: PCRE (and JIT) is a recursive, depth-first engine, so it needs a stack where
274: the local data of the current node is pushed before checking its child nodes.
275: Allocating real machine stack on some platforms is difficult. For example, the
276: stack chain needs to be updated every time if we extend the stack on PowerPC.
277: Although it is possible, its updating time overhead decreases performance. So
278: we do the recursion in memory.
279: </P>
280: <P>
281: (2) Why don't we simply allocate blocks of memory with <b>malloc()</b>?
282: <br>
283: <br>
284: Modern operating systems have a nice feature: they can reserve an address space
285: instead of allocating memory. We can safely allocate memory pages inside this
286: address space, so the stack could grow without moving memory data (this is
287: important because of pointers). Thus we can allocate 1M address space, and use
288: only a single memory page (usually 4K) if that is enough. However, we can still
289: grow up to 1M anytime if needed.
290: </P>
291: <P>
292: (3) Who "owns" a JIT stack?
293: <br>
294: <br>
295: The owner of the stack is the user program, not the JIT studied pattern or
296: anything else. The user program must ensure that if a stack is used by
297: <b>pcre_exec()</b>, (that is, it is assigned to the pattern currently running),
298: that stack must not be used by any other threads (to avoid overwriting the same
299: memory area). The best practice for multithreaded programs is to allocate a
300: stack for each thread, and return this stack through the JIT callback function.
301: </P>
302: <P>
303: (4) When should a JIT stack be freed?
304: <br>
305: <br>
306: You can free a JIT stack at any time, as long as it will not be used by
307: <b>pcre_exec()</b> again. When you assign the stack to a pattern, only a pointer
308: is set. There is no reference counting or any other magic. You can free the
309: patterns and stacks in any order, anytime. Just <i>do not</i> call
310: <b>pcre_exec()</b> with a pattern pointing to an already freed stack, as that
311: will cause SEGFAULT. (Also, do not free a stack currently used by
312: <b>pcre_exec()</b> in another thread). You can also replace the stack for a
313: pattern at any time. You can even free the previous stack before assigning a
314: replacement.
315: </P>
316: <P>
317: (5) Should I allocate/free a stack every time before/after calling
318: <b>pcre_exec()</b>?
319: <br>
320: <br>
321: No, because this is too costly in terms of resources. However, you could
322: implement some clever idea which release the stack if it is not used in let's
323: say two minutes. The JIT callback can help to achive this without keeping a
324: list of the currently JIT studied patterns.
325: </P>
326: <P>
327: (6) OK, the stack is for long term memory allocation. But what happens if a
328: pattern causes stack overflow with a stack of 1M? Is that 1M kept until the
329: stack is freed?
330: <br>
331: <br>
332: Especially on embedded sytems, it might be a good idea to release
333: memory sometimes without freeing the stack. There is no API for this at the
334: moment. Probably a function call which returns with the currently allocated
335: memory for any stack and another which allows releasing memory (shrinking the
336: stack) would be a good idea if someone needs this.
337: </P>
338: <P>
339: (7) This is too much of a headache. Isn't there any better solution for JIT
340: stack handling?
341: <br>
342: <br>
343: No, thanks to Windows. If POSIX threads were used everywhere, we could throw
344: out this complicated API.
345: </P>
1.1.1.2 ! misho 346: <br><a name="SEC10" href="#TOC1">EXAMPLE CODE</a><br>
1.1 misho 347: <P>
348: This is a single-threaded example that specifies a JIT stack without using a
349: callback.
350: <pre>
351: int rc;
352: int ovector[30];
353: pcre *re;
354: pcre_extra *extra;
355: pcre_jit_stack *jit_stack;
356:
357: re = pcre_compile(pattern, 0, &error, &erroffset, NULL);
358: /* Check for errors */
359: extra = pcre_study(re, PCRE_STUDY_JIT_COMPILE, &error);
360: jit_stack = pcre_jit_stack_alloc(32*1024, 512*1024);
361: /* Check for error (NULL) */
362: pcre_assign_jit_stack(extra, NULL, jit_stack);
363: rc = pcre_exec(re, extra, subject, length, 0, 0, ovector, 30);
364: /* Check results */
365: pcre_free(re);
366: pcre_free_study(extra);
367: pcre_jit_stack_free(jit_stack);
368:
369: </PRE>
370: </P>
1.1.1.2 ! misho 371: <br><a name="SEC11" href="#TOC1">SEE ALSO</a><br>
1.1 misho 372: <P>
373: <b>pcreapi</b>(3)
374: </P>
1.1.1.2 ! misho 375: <br><a name="SEC12" href="#TOC1">AUTHOR</a><br>
1.1 misho 376: <P>
377: Philip Hazel (FAQ by Zoltan Herczeg)
378: <br>
379: University Computing Service
380: <br>
381: Cambridge CB2 3QH, England.
382: <br>
383: </P>
1.1.1.2 ! misho 384: <br><a name="SEC13" href="#TOC1">REVISION</a><br>
1.1 misho 385: <P>
1.1.1.2 ! misho 386: Last updated: 08 January 2012
1.1 misho 387: <br>
1.1.1.2 ! misho 388: Copyright © 1997-2012 University of Cambridge.
1.1 misho 389: <br>
390: <p>
391: Return to the <a href="index.html">PCRE index page</a>.
392: </p>
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